Pollution caused by pesticides is becoming relevant because of their harmful environmental effects. The persistence, bioaccumulation and toxicity of some organochloride pesticides have resulted in their restricted use since 1970 and a requirement to monitor them in many countries. Pesticides have endocrine, immunological, reproductive and carcinogenic effects in both humans and animals. The facilitated infiltration of substances results in the pollution of hydric underground resources in karstic limestone such as that found in the state of Yucatan. Observing the north occidental region of the state of Yucatan is particularly important as it is characterized by agricultural activities (wide use of pesticides), significant human settlements and underground water flows oriented towards the north coast. In this study, the underground water quality of a karstic aquifer was evaluated by quantifying the presence of organochlorine pesticides in 29 wells located throughout the Mérida‐Progreso transect, Yucatan, Mexico. The presence of DDT, lindane and their metabolites was detected at concentrations above the permissible limits stated by Mexican regulatory standards (NOM‐127‐SSA1‐1994 2010) in the majority of wells studied. Continuous monitoring of the underground hydric resources in this region is therefore essential to raising awareness of pollution risks and the vulnerability of the coastal north to the contamination of the underground water flows.

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